1. Field of the Invention
The present invention relates to a logical volume management method and a logical volume management program of a storage system used for a computer system, and a computer system.
2. Description of the Related Art
A storage system generally includes randomly accessible nonvolatile storage media, such as magnetic disk and optical disk. The most common storage system at present has many compact-size disk drives. On the other hand, as semiconductor technology advances, there has been developed a nonvolatile semiconductor memory that can retain data even after turning off a power supply and in which batch erasing can be performed (i.e. all data can be erased at a time).
Among nonvolatile semiconductor memories on which batch erasing can be performed, there can be mentioned a flash memory and EEPROM (Electrically Erasable Programmable Read Only Memory). In these nonvolatile memories, complete erasing of data on a chip (i.e. a complete erasing function) can be implemented by electrically erasing data at a time on the basis of chip unit on the memory (i.e. performing chip erasing). The flash memory is a semiconductor memory that is nonvolatile and readable like a read only memory (ROM), yet writable like a random access memory (RAM). The storage system having flash memories as storage media is excellent in service life, power-saving, access time and the like as compared with a storage system having many compact-size disk drives.
U.S. Pat. No. 6,529,416, which is incorporated herein by reference, discloses a technique in which a flash memory drive having a plurality of flash memories that are accessible by a conventional access means such as a hard disk drive in SCSI and the like, is used instead of the hard disk drive of a storage system.
In a computer system, complete erasing of data on a storage system is often performed, for the purpose of preventing leakage of personal data or business data that a company possesses. Data once stored on a hard disk included in a storage system cannot be completely erased by a standard erasing function provided in an OS or formatting of a hard disk. In order to perform complete erasing of data on the hard disk, overwriting of fixed pattern data should be repeated several times.
In the computer system disclosed in the above-mentioned patent document in which a flash memory drive is used instead of the hard disk drive of the storage system, in order to perform complete erasing of data on a logical volume allocated to the flash memory drive, overwriting of data on the flash memory drive should be repeated several times.
In addition, a data write speed onto a flash memory that included in a flash memory drive is slower than that onto a hard disk. Therefore, when overwriting of data is repeated several times, there arises a problem that a time period for performing complete erasing of logical volume on the flash memory drive becomes longer than a time period for performing complete erasing of logical volume on the conventional hard disk.
Further, a flash memory has a limitation in data rewrite count. When overwriting of data is repeated several times and complete erasing of logical volume on a flash memory drive is repeatedly performed, there arises a problem that a possible count of data rewriting of flash memory drive is wasted.
Therefore, it would be desirable to provide a method for logical volume management of a storage system, a logical volume management program and a computer system, that can reduce a time period for performing complete erasing of logical volume on a flash memory drive, and further can reduce rewrite count on a flash memory upon performing complete data erasing.